Optically transparent glass and/or plastic fibers are being used advantageously in diverse areas of data communication and in other fields which require transfer of light energy between two locations. Such use has resulted in the need for convenient, reliable and efficient apparatus and techniques for coupling a pair of such fibers to each other. The difficulty in coupling optical fibers arises largely from their very small cross-section. In order to obtain highly efficient transfer of light energy from one optical fiber to another, the cores of the fibers must be positioned in axial alignment with each other and suitably close together. Since optical fiber cores typically have a diameter on the order of 50 .mu.m, coupled optical fibers must be positioned with great precision. A further difficulty arises from the great fragility of such small hair-like fibers.
Optical fiber coupling apparatus and techniques found in the prior art are reviewed by C. Kleekamp and B. Metcalf in "Designer's Guide to Fiber Optics--Part 4," Electronic Design News, pages 51-62 (Mar. 5, 1978).
The coupling apparatus and techniques of the prior art may be divided into three types: the fiber splice; the alignment adjustable connector; and the self-aligned connector. A fiber splice is generally made by bringing two fibers into butted alignment through the use of a guiding structure. The two fibers and the guiding structure are then all permanently glued together in the aligned position with an index-matching adhesive. Guiding structures which have been used for splicing include V-shaped grooves, a square tube, and a bundle of three parallel rods which are 6.464 times larger in diameter than the fibers. The disadvantages of splices are that they form a permanent coupling of the fibers and that they are not generally convenient to install in the field.
Optical fiber connectors have the advantage that a permanent coupling is not made. Connectors are taught, for example, in U.S. Pat. Nos. 3,936,143 and 4,019,806. The disadvantages of adjustable connectors are their complexity and the inherent need to make a cumbersome manual adjustment which requires alignment monitoring apparatus. The need to make a manual alignment makes this type of connector very difficult to use in the field.
Optical fiber connectors which are automatically aligned are, in principle, readily usable in the field. Most use cylinders and cones to automatically align and hold the fibers. One approach is to use a concentric sleeve and locking nuts to align and hold two ferrules. Each ferrule carries an optical fiber in concentric relationship therewith. A bundle of three or four rods within the ferrule has been used to center the fiber within the ferrule. Unfortunately, concentric sleeve connectors are complex and expensive.
It is an object of this invention to provide a self-aligning optical fiber plug connector which has low optical energy loss even after many reconnection operations.
It is another object to provide such a connector at low cost.
Still another object is to provide a connector of this type which is simple to use and reliable, even in field use.
A further object is to provide a durable self-aligning optical fiber connector which also protects the fiber end from deterioration while the plug connection is being made as well as before and after connection.
It is also an object to provide a self-aligning optical fiber connector which avoids the use of reference surfaces which are rounded.